The Boundary Treatment for Local Grid Refinement of Inundation Simulations

The meteorological and geographical conditions in Taiwan frequently cause inundation in the midstream and downstream floodplain when storm occurs. It usually takes losses of people’s wealth and life. Owing to the large amount computation requirements on the two-dimensional inundation simulation in large areas with fine resolution in dense population areas, the down-scale inundation simulation using local refinement grid at the dense population areas could save the time of model calculation. The main purpose of the study is to find a reasonable boundary treatment for the local area of down-scale inundation simulation which is higher resolution in topography given by the Digital Terrain Model. Because of the higher resolution in local areas, the boundary condition between fine grids and coarse grids is not consistent. In the boundary between coarse and fine grids, the fine grids discharges are calculated by the coarse grid discharges and the allocated weighting factors. The weighting factors are equal-discharge, equal-velocity, Chezy’s formula and Manning’s formula. The simulation results and computer run time among the four weighting factors are compared in the study. The research area is the Ba-zhang Creek Basin. The study compares boundary treatments by the error correction of simulation. The result is not only raising the efficiency of simulation, but also improving the accuracy of simulation error to close the level of fine-grid simulation in the whole area. For the real-time inundation early-warning system, the high efficiency of model could provide inundation information to assist the disaster reduction for emergency management agency.